This invention relates to a method and apparatus for improving the quality of the reception of motion pictures and, more particularly, to an improved method and apparatus for interpolating motion picture images between images of a sequence comprising a motion picture.
In a motion picture, motion is simulated by a sequence of images at spaced time intervals typically at a rate of 24-30 images per second. Frame rates less than 24-30 frames per second are sometimes used because of bandwidth limitations, such as Internet applications, or because of economic or data storage limitations. However, when the frame rate is reduced much below 24 frames per second, the quality of the perception of the motion picture is degraded. Specifically, moving objects, instead of appearing to move continuously in the scene, are perceived to have a jerky motion in which the objects move in a series of abrupt transitions from position to position in the displayed scene.
In Internet applications and in other applications in which the bandwidth is limited, systems have been designed to enable a low frame rate to be transmitted by generating the picture at a high frame rate, determining motion vectors between the frames of the motion picture representing the motion of the objects from frame to frame in the motion picture, then transmitting only every other frame or less to the receiver over the communication channel along with the motion vectors. The motion vectors and the transmitted frames are then used to generate intervening frames which correspond to the frames that were eliminated from the motion picture at the transmitter and then the sequence of images comprising the transmitted frames and interpolated frames are then displayed as a motion picture at the receiver.
The above-described system is effective in eliminating the jerky motion as perceived by the viewer, but it requires a specially designed transmitter equipment to generate the motion vectors and the motion vectors use up bandwidth in the transmission channel.
In a preferred system of the present invention, jerky motion perception is eliminated from low frame rate motion pictures without the need of special transmitting equipment and without the need for motion vectors to be transmitted to the receiver from a transmitter. The system of the invention in fact requires no transmitter and, in many applications, has no transmitter. In accordance with the invention, the motion of image elements, in a motion picture represented by a sequence of motion picture frames, is detected. The term xe2x80x9cimage elementxe2x80x9d as used herein refers to a pixel sized element of a depicted scene and objects in that scene whereby an image element representing a part of an object which is moving is considered to move with the object. The motion picture may be a sequence of images at a low frame rate. In accordance with the invention, a dense vector field of forward vectors representing the changes in positions of image elements from each frame to each succeeding frame in the sequence are computed. In addition, a dense field of backward vectors are detected for the changes in position of the image elements from each frame to the preceding frame. The forward vectors are scaled to a fraction of their original magnitude and motion adjusted images are generated from the scaled forward vectors by moving each image element in the first frame to positions in the motion adjusted images as indicated by the scaled forward vectors. In addition, one or more second motion adjusted images are generated by scaling the backward vectors by a fraction of their original magnitude and moving the image elements in the succeeding frame to positions in the second motion adjusted images in accordance with the scaled backward vectors. The motion adjusted images are then merged into interpolated frames. The above process is repeated for each successive overlapping pair of adjacent frames in the motion picture sequence. The interpolated frames are interleaved with the original frames and the resulting sequence is displayed to display the motion picture with the jerky motion eliminated or greatly reduced. In a specific embodiment, one interpolated frame is generated for each pair of adjacent frames to be positioned in time halfway between the corresponding pair of frames. Accordingly, in this system, the forward and backward vectors are scaled by onehalf to correspond to the position of the interpolated frame.